(1) Field of the Invention
The present invention relates to describe a vehicle recovery assembly for underwater vehicles which operate under negatively buoyant conditions.
(2) Description of the Prior Art
A variety of recovery systems for underwater vehicles have been in operation since submersibles were first conceived and operated. More recently, the Navy has operated vehicles employing recovery systems designed to bring negatively ballasted vehicles to the surface upon conclusion of vehicle operations.
As indicated by the references that follow, present recovery systems rely on inflating bags (attached to the vehicle) with lower density gas or liquid, relative to seawater. The inflated bags provide sufficient positive buoyancy to lift the vehicle to the surface. The low density gas or liquid, can be stored internal to the vehicle at high density, where upon a command the fluid expands to a low density state into the recovery floats external to the vehicle.
The principle of buoyant bag recovery is straightforward, although complications arise for vehicles operating at speeds greater than 5 knots. Complications arise due to the hydrodynamic loading, which will occur when the buoyancy floats expand into the hydrodynamic flow past the vehicle. Under these circumstances, the forces are sufficient to damage the recovery bags, thus necessitating the use of exotic materials of construction for the bag. The materials are typically expensive, all but negating the possibility of having an affordable recovery system.
Furthermore, in order to retrieve the undersea vehicle after recovery from the surface water and subsequently prepare the vehicle for another operation, the entire recovery assembly must be replaced from within the vehicle, requiring excessive disassembly of the vehicle, another undesirable cost driver.
In Radford (U.S. Pat. No. 3,706,294), a recovery assembly conforming to the outer contour of a torpedo is disclosed. Compressed gas inflates an annular member that operates as a buoyancy device. A similar configuration with similar limitations exists in Sandler (U.S. Pat. No. 4,271,552) where a torpedo recovery assembly having an inflatable annular sleeve 28 is used to slow the torpedo and raise the torpedo to the water's surface.
In Driggs (U.S. Pat. No. 1,998,805), a torpedo recovery assembly is disclosed. In the cited reference, an inflatable bag 52 is pressurized when the carrying torpedo decelerates and the torpedo begins to sink in an undersea environment. The increased pressure at increased depths acts upon a diaphragm to allow air to inflate the bag 52 thereby opening external doors 55 and 56 to a buoyant bag 16. At least one limitation on device of the Driggs reference is that the doors may further decelerate the torpedo but as a result of an initial deceleration. The doors do not act to decelerate the torpedo initially.
An improvement to the recovery systems described above would be an assembly that could decelerate a torpedo or undersea vehicles from velocities in excess of five knots to deploy a buoyant recovery device. The assembly should be a lower cost alternative to present buoyant recovery systems, whereby the concept is based on a simple design employing single components designed to perform multiple and different functions, thus reducing complexity, increasing reliability and reducing overall cost of operation. The assembly should allow a relatively straight forward recovery of the torpedo or underwater vehicle via surface ship or some other means other than submerged recovery.